Re: RE: Delivery Dates

Les,
This is not rocket science, but...just a few comments. I think you can
come up with a guess-timate on your proposed project.
First look up what the wind area is for your HF beam, and the antennas
going on the satellite elevation boom. All commercial mfrs publish this if
you look hard. Then check what US Tower rates the tower for in wind area.
They probably rate the tower for a certain wind area at a certain wind
speed. Some will do this for more than one windspeed.
Lets say the tower is rated for 16 square foot at 50-mph and less at
70-mph. Your HF yagi might be 12 sq-ft, a 2m yagi 3 sq-ft and a 432 yagi 2
sq-ft this is a total of 17 sq-ft. You should not have problems at winds
up to 50-mph, and supposedly, you can lower the tower if higher winds are
predicted. Adding guy lines will raise the tower wind-load rating. If you
plan on a small dish for 2.4 GHz you need to add that into your calculation
area = pi*R^2. A two-foot dish will have 12 sq-ft of wind area...but you
can reduce that by stowing it in the "bird-bath" position.
The Orion is definitely capable of handling all the load you will have. I
suppose that it will be mounted internal to the tower and the normal
position is usually about 3-foot below the tower top (determined by the
tower mfr). Since the Orion is a big non-std rotator you should check if
it will fit inside the tower. Most tower makers assume you will be using a
rotator like the Ham-IV or similar series.
The rotator rating increases when installed interior to the tower when used
with a thrust bearing. If you have 5-feet exposed and 3-feet inside the
tower the loads are nearly equal. The load of the HF beam placed just
above the thrust bearing will have less loading on the rotator than the
satellite antennas. The elevation rotator will take full force of the
satellite antennas. I have used a B5400 mounted 10-foot above the tower
with an 18-fot boom 436CP42, 12-foot boom 1296 yagi, and 33-inch dish up to
65-mph wind with not ill effects (other thant the small tripod tower blew
over due to inadequate mounting to the roof). Again, being able to retract
the tower is your best way to avoid problems in wind.
Do use a strong steel (not aluminum) azimuth mast to carry the load. My
four 21-foot 2m crossed eme-yagis on a 12-by-12 foot "H-frame" result in
approx. 16 sq-feet of wind area. They are supported 3-feet above the
thrust bearing on a sched-80 2-inch steel pipe. This sits on top of a
guyed 50-foot Rohn-25 tower...well beyond its wind rating. I can lower it
for high winds uisng a hazer-lift system...but this has to be done before
the wind starts as I have to disconnect the guy lines to lower it. This
array survived a 30-hour long wind storm in 2003 with sustained windspeeds
of 65-mph!
I do think placing satellite antennas on a high tower is not the best
approach, since they are high maintenance vs regular HF and FM yagis.
Running long coax lines at VHF or higher is not simple on a crank-up tower.
At 1296 one should either mount the 1296 radio gear up at the antenna or
run low-loss lines like 7/8-inch hardline. Otherwise, you will be lucky to
see 25% of your transmit power reach the antennas. Hardline cannot be run
on a tower that lowers.
So that is my best advice. GL on your project!
73's Ed - KL7UW
PS: veiw photo of my 2m-eme array at: http://www.qsl.net/al7eb/eme144.htm
At 11:21 AM 4/22/2005 -0400, sco@sco-inc.com wrote:
>Freeman, for some reason your ISP thinks my email address is a spammer. My
>last email to you was rejected but there was no way mentioned to report the
>error to your ISP.
>
>>If this is the route you are taking then be sure to purchase the chormolly
>>mast, or at the very least the reinforced mast. Check with US-Towers
>>on the load capacity of the mast that sticks out above the tower.
>
>I think that is a good idea. I have asked US Towers what they think of my
>proposed idea.
>
>>I would still recommend looking at the HDX version of the tower, as I have.
>>You can save a bit of money on the tower buy purchasing through one of
>>US-Towers dealers (like Texas Towers). I've noticed a $500 to $800 price
>>difference between the prices on US Towers web site and Texas Towers
>>quotes.
>
>I agree. HRO is several hundred dollars lower. But the extra cost of a HDX
>tower is about the same as two separate TX towers (55 ft for HF and 72 ft
>for sat). Then I would have no big advantage of using just one tower. The
>M2 Orion 2800 AZ rotor can handle 35 sq ft so it should handle the extra
>windload of the mast and small satellite array. If I leave the tower down
>at the 23 ft height, except when i am using it I still think (on paper)
>that would be more than adequate???
>
>Les
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73's,
Ed - KL7UW <new call>
=================================
http://www.qsl.net/al7eb
144-MHz EME - BP40iq:
FT-847, mgf-1801/1402, 4xM2-xpol-20, 170w
=================================
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